So-called stack-type nonvolatile semiconductor memory devices are known. Such memory devices include the NAND flash memory which is manufactured by a manufacturing process of BiCS techniques. The manufacturing process of BiCS techniques include laminating gate electrodes and interlayer insulation films alternatively, forming holes through them from the top layer to the bottom layer, and burying the holes with impurity-doped silicon. As a result, the gate insulation layers surround each silicon pillar at intervals. With memory films such as silicon nitride films formed at the intersections of the pillar and gate insulation films beforehand, NAND memory cells can be formed. Serially-connected vertical transistors thus formed at the intersections of the electrode plates and a silicon pillar forms a memory string.
The NAND flash memory incorporating BiCS techniques (BiCS flash memory) includes of a so-called pipe type (p-BiCS flash memory). In the p-BiCS flash memory, the bottoms of a pair of adjacent memory strings are connected via a transistor called a pipe layer. The tops of the pair of the memory strings are connected to a bit line and a source line via a select gate, respectively.
The p-BiCS flash memory does not contain bottoms of the holes, and therefore a process for removing the memory film at the bottom of the hole is unnecessary, which results in such memory films unharmed and excel in reliability. Moreover, unlike a so-called line-type BiCS flash memory, select gate transistors and source lines are formed after a heating step for forming the memory films. For this reason, the characteristics of the select gate transistors can be improved, low-resistance metal source lines can be applied, and reading required for operation in a large-scale chip can be performed.
The p-BiCS flash memory can have higher integration than conventional NAND flash memories. However, much higher integration and simplified manufacturing process and design are always required for semiconductor devices. This also applies to the p-BiCS flash memory.